Impingement cooling device for a laser disk and associated laser disk module

ABSTRACT

Impingement cooling devices for a laser disk include a carrier plate on the front side of which the laser disk can be secured, and a supporting structure, on the front side of which the rear side of the carrier plate is secured. The supporting structure has a plurality of cooling liquid feed lines from which the cooling liquid emerges in the direction of the rear side of the carrier plate and a plurality of cooling liquid return lines. The feed and return lines run parallel to one another in the longitudinal direction of the supporting structure, and the supporting structure includes a plurality of cutouts or the rear side of the carrier plate that are open toward the supporting structure, and the cooling liquid feed lines lead into and the cooling liquid return lines lead away from the plurality of cutouts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35U.S.C. § 120 from U.S. patent application Ser. No. 16/148,269, filed onOct. 1, 2018, which is a continuation of PCT Application No.PCT/EP2017/056992 filed on Mar. 23, 2017, which claims priority fromGerman Application No. DE 10 2016 205 638.7, filed on Apr. 5, 2016. Theentire contents of each of these priority applications are incorporatedherein by reference.

TECHNICAL FIELD

The invention relates to an impingement cooling device for a laser disk.

BACKGROUND

Usually, laser disks are glued onto disk-shaped heat sinks (diskcarriers) that are cooled on the rear side by impingement flow. Thethermomechanical properties of the disk carrier substantially determinethe thermal lens effect of the laser disk. This leads to demandingrequirements for the thermal conductivity and stiffness of the diskcarrier, which is therefore made of chemical vapor deposition (CVD)diamond. For higher laser power outputs, this leads to thicker diamonddisks and high production costs. In other words, greater stiffness withalmost the same heat resistance is achieved by ever thicker diamonddisks.

An impingement cooling device disclosed in US 2014/0190665 A1 has asingle cutout adjoining the rear side of the carrier plate, and radiallyrunning return lines.

In the impingement cooling device disclosed in WO 2011/130897 A1, alaser disk is mounted on a carrier plate, which at the same time forms aresonator mirror of a laser resonator. A cooling liquid emerging from anozzle opening impinges on the self-supporting rear side of the carrierplate, which is thereby cooled.

EP 1 213 801 A2 discloses a cooling device in which the laser-activesolid body is cooled directly with cooling water on its rear side, whichis provided with a covering layer.

U.S. Pat. No. 6,339,605 B1 discloses a cooling arrangement for a laserdisk mounted on a copper substrate. A cooling liquid flows through thecopper substrate and is conducted into micro-channels of the coppersubstrate that are open toward the laser disk. The rear side of thelaser disk is consequently cooled by the cooling liquid flowing throughthe micro-channels.

Furthermore, US 2007/0297469 A1 discloses a cooling arrangement for alaser disk mounted on a carrier plate of diamond or sapphire. Within thecarrier plate, micro-channels for a cooling liquid run near the surface.

SUMMARY

Advantages of the current disclosure include an impingement coolingdevice with a greater stiffness of the carrier plate and at the sametime almost the same heat resistance of the carrier plate, withouthaving to increase the thickness of the (diamond) carrier plate. Theseadvantages are achieved by a carrier plate configured to secure thelaser disk on a front side and having a rear side, an impingementcooling area for cooling the carrier plate by a cooling liquid, asupporting structure secured on a front side thereof to the rear side ofthe carrier plate. The supporting structure has a plurality of coolingliquid feed lines from which the cooling liquid emerges towards the rearside of the carrier plate, feed and return lines that run parallel toone another in the longitudinal direction of the supporting structure. Aplurality of cutouts in a region adjoining the rear side of the carrierplate that are closed toward the rear side of the carrier plate, and thecooling liquid feed lines lead into the plurality of cutouts and thecooling liquid return lines lead away from the plurality of cutouts andwherein the feed lines are each formed by a separate tube that isarranged in a through-channel of the supporting body, and the returnlines in the supporting body are respectively formed by a gap betweenthe through-channel and the tube, or vice versa

In one aspect, a carrier plate (for example of diamond material) isattached to a stiffening rear-side supporting structure (for example oftungsten carbide or aluminum nitride) through which cooling liquid flowsto retain the small heat resistance of a diamond heat sink. Since theheat resistance of the supporting structure does not influence thetemperature of the laser disk, materials with great stiffness and withrelatively high heat resistance can be used here.

Finite element method (FEM) calculations have shown that a carrier plateof CVD diamond about 2 mm thick and a rear-side supporting structure oftungsten carbide have a mechanical resistance to a thermally inducedbending of the laser disk that is approximately equal to a carrier plateof CVD diamond about 10 mm thick that is not supported on the rear side.Furthermore, the FEM calculations have shown that a carrier plate ofpolycrystalline diamond composite (PDC) about 2 mm thick and a rear-sidesupporting structure of tungsten carbide have a mechanical resistance tothermally induced bending of the laser disk that is approximately equalto a carrier plate of CVD diamond about 3.4 mm thick that is notsupported on the rear side.

The cutouts in the supporting structure may either be open toward therear side of the carrier plate, so that the cooling liquid impingesdirectly on the rear side of the carrier plate (direct heat transfer ofthe carrier plate into the cooling liquid), or else be closed toward therear side of the carrier plate, so that the cooling liquid impinges on abase of the carrier plate. In the latter case, direct contact betweenthe cooling liquid and a solder located between the carrier plate andthe supporting structure is avoided, and as a result, the risk ofcorrosion is reduced.

The carrier plate can be formed from diamond material (for example CVDdiamond or polycrystalline diamond composite (PDC)) and has a thicknessof at most 5 mm, e.g., at most 3 mm, or at most 2 mm. The diamondmaterial offers high thermal conductivity and at the same time enoughintrinsic stiffness to prevent the form of the laser disk that ismounted on the front side from being influenced significantly by thecooling structures on the rear side. Depending on the material pairing,the carrier plate and the supporting structure are soldered, glued, orsintered to one another or connected to one another by so-calledbonding, e.g., by a mechanically load-bearing, rigid connection betweentwo solid bodies without the formation of an intermediate layer.

In some embodiments, the rear side of the carrier plate is secured onthe front side of a distributor plate, which has the cutouts, whereinthe rear side of the distributor plate is secured on a supporting body,which has the feed and return lines. The supporting body can be formedfrom ceramic or hard metal and has a thickness of at least 1 cm, e.g.,between 2 cm and 10 cm. Advantageously, the cutouts extend asthrough-openings to the rear side of the distributor plate.Alternatively, the distributor plate may also have upstream of itscutouts nozzle openings that are directed toward the rear side of thecarrier plate, typically at right angles with respect to the rear sideof the carrier plate. The distributor plate can be formed either fromdiamond material or from ceramic or hard metal (for example tungstencarbide or aluminum nitride), and have a thickness of at least 0.3 mm,e.g., at least 0.5 mm.

The cutouts in the distributor plate may be open toward the rear side ofthe carrier plate, and extend as through-openings from the front side tothe rear side of the distributor plate, so that the cooling liquidimpinges on the rear side of the carrier plate, or else be closed by abase of the distributor plate, so that the cooling liquid impinges onthe base of the distributor plate.

In some embodiments, arranged between the distributor plate and thesupporting body is a nozzle plate with nozzle openings, which connectthe feed lines of the supporting body respectively to the cutouts in thedistributor plate and are aligned in the direction of the rear side ofthe carrier plate, e.g., at right angles with respect to the rear sideof the carrier plate, and with through-openings, which connect thecutouts in the distributor plate to the return lines. Through the nozzleopening, the cooling liquid is made to impinge at an accelerated rate onthe rear side of the carrier plate. The nozzle plate can be formed fromdiamond material (for example CVD or PDC diamond), ceramic or hard metal(for example tungsten carbide or aluminum nitride) and has a thicknessof at least 0.3 mm, e.g., at least 0.5 mm.

Depending on the material pairing, the individual components of thesupporting structure are respectively soldered, for example bycopper-based and/or silver-based hard solder, or else glued, sintered orbonded to one another.

In other embodiments, the rear side of the carrier plate has the cutoutsand is secured on the front side of a supporting body, which has thefeed lines and return lines. A carrier plate of CVD diamond can beprovided with the cutouts for bearing the impact of the impingement flowon the rear side, for example by laser machining, and then a shaft, forexample of tungsten carbide, can be soldered onto the structured rearside with hard solder. Subsequently, the required feed and return linescan be introduced into the tungsten carbide by spark erosion.Alternatively, the supporting body can also be made of individualperforated disks that are cut to size by a laser and soldered togetherto form a stack and the holes of which are in line with one another toform continuous feed and return lines in the stack.

The supporting body can be formed from ceramic or hard metal (forexample tungsten carbide or aluminum nitride) and has a thickness of atleast 0.5 cm, e.g., between 0.5 cm and 10 cm, to increase the stiffnessof the carrier plate to a sufficient extent.

In some embodiments, the feed and return lines in the supporting bodyare formed by through-channels, that are introduced, for exampledrilled, into the supporting body next to one another. In someembodiments, the feed lines in the supporting body are, by contrast,respectively formed by a separate tube (for example nozzle needle),arranged in a through-channel of the supporting body to form an(annular) gap. The return lines in the supporting body are respectivelyformed by the (annular) gap that is present between the through-channeland the tube. In this case, the feed line is surrounded by just onesingle return line in the form of a ring or part-ring, which in the caseof a return line in the form of a ring results in a homogeneous spatialdistribution of the cooling. Alternatively, the return lines mayconversely also be respectively formed by a separate tube (for examplenozzle needle) in a through-channel of the supporting body and the feedlines may be respectively formed by the (annular) gap that is presentbetween the through-channel and the tube.

Each of the feed lines is surrounded by a plurality of return lines,e.g., point-symmetrically in relation to the feed line, wherein thereturn lines in turn lead away from that cutout in the distributor plateinto which the feed line surrounded by them leads. In other words, aplurality of return lines are assigned to each feed line, which resultsin a homogeneous spatial distribution of the cooling. However, aninhomogeneous spatial distribution of the cooling, for example due toonly one return line per feed line, may also be used if the material ofthe carrier plate allows sufficient heat spreading within the carrierplate.

Advantageously, the feed and return lines run parallel to one another inthe longitudinal direction of the supporting structure, e.g., in thecase of a supporting body in the direction of the thickness thereof.

In some embodiments, a laser disk module with an impingement coolingdevice formed as described herein has a laser disk that is secured onthe front side of the carrier plate of the impingement cooling device.

Further advantages and advantageous refinements of the subject matter ofthe invention emerge from the description, the claims and the drawing.Similarly, the features mentioned above and features still to be set outcan each be used on their own or together in any desired combinations.The embodiments shown and described should not be understood as anexhaustive list, but rather are of an exemplary character for thedescription of the invention.

DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B show a first exemplary embodiment of the impingementcooling device for a laser disk in the mounted state (FIG. 1A) and in anexploded view (FIG. 1B).

FIG. 2 shows a schematic longitudinal section through the impingementcooling device of FIG. 1 in the region of a feed line arranged betweentwo return lines.

FIG. 3 shows a second exemplary embodiment of the impingement coolingdevice in a schematic longitudinal section analogous to FIG. 2.

FIG. 4 shows a third exemplary embodiment of the impingement coolingdevice in a schematic longitudinal section analogous to FIG. 2.

FIG. 5 shows a fourth exemplary embodiment of the impingement coolingdevice in a schematic longitudinal section analogous to FIG. 2.

In the following detailed description, identical reference signs areused for components that are the same or functionally the same in thefigures.

DETAILED DESCRIPTION

The impingement cooling device 1 shown in FIGS. 1A and 1B serves forcooling a laser disk 2 of a disk laser (not shown) by a cooling liquid.The laser disk 2 is formed from laser-active gain material and may befor example a Yb:YAG Yb:LuAG Yb:YAG Yb:YLF, Yb:Lu₂O₃, Yb:LuAG Yb:CALGO,Nd:YAG or Nd:YVO₄ crystal with a thickness of about 50 μm to about 500μm.

The impingement cooling device 1 includes a disk-shaped carrier plate 3,on the front side 3 a of which is secured a laser disk 2, and arear-side supporting structure 4, on which the rear side 3 b of thecarrier plate 3 is secured. The supporting structure 4 has a disk-shapeddistributor plate 5, a disk-shaped nozzle plate 6 and a cylindricalsupporting body (supporting block) 7 with a diameter of about 25-40 mm.The rear side 3 b of the carrier plate 3 is secured on the front side 5a of the distributor plate 5, the rear side 5 b of which is in turnsecured on the front side 6 a of the nozzle plate 6. The rear side 6 bof the nozzle plate 6 is secured on the front side 7 a of the supportingbody 7.

The carrier plate 3 is formed from a diamond material, for example fromCVD diamond or polycrystalline diamond composite (PDC), which has a highthermal conductivity and at the same time a sufficiently great intrinsicstiffness to avoid significant influencing of the form of the laser disk2 mounted on the front side 3 a by rear-side cooling structures.Typically, the carrier plate 3 is about 2-4 mm thick.

The distributor plate 5 has a plurality of cutouts 8 that are open bothtoward the rear side 3 b of the carrier plate 3 and the front side 6 aof the nozzle plate 6, which therefore extend as through-openings fromthe front side 5 a to the rear side 5 b of the distributor plate 5. Tooptimize the cooling characteristics, the distributor plate 5 maylikewise be formed from a diamond material (for example CVD or PDCdiamond) or alternatively from ceramic or hard metal (for exampletungsten carbide or aluminum nitride). Typically, the distributor plate5 is about 0.5 mm thick.

The nozzle plate 6 is formed from ceramic or hard metal and has aplurality of small nozzle openings 9 and a plurality of through-channels10, wherein each nozzle opening 9 is surrounded by a plurality ofthrough-channels 10. The nozzle openings 9 are respectively directed atright angles to the rear side of the carrier plate 3. Typically, thenozzle plate 6 is about 0.5 mm thick.

The supporting body 7 is formed from ceramic or hard metal (for exampletungsten carbide or aluminum nitride) and has a plurality of coolingliquid feed and return lines 11, 12 formed as through-channels, with aline diameter of 0.3-5 mm (e.g., 3 mm), that run parallel to one anotherin the direction of the thickness of the supporting body 7. Each feedline 11 is surrounded by a plurality of return lines 12, here, by way ofexample, six. Each feed line 11 leads via one of the nozzle openings 9in the nozzle plate 6 into one of the cutouts 8 in the distributor plate5. From each cutout 8 there lead away in turn via the through-channels10 of the nozzle plate 5 to the six return lines 12 that surround thefeed line 11 leading into this cutout 8. Typically, the supporting body7 is between 0.5 cm and 10 cm thick.

Depending on the material pairing, soldering, gluing, sintering, orbonding processes are used to connect the individual components 3 and5-7 of the impingement cooling device 1. When choosing solder,compatibility between the solder and the cooling circuit with respect tocorrosion should be considered. Typically, therefore—and also because oftheir strong adhesive bonding, high strength, and stiffness—copper-basedand/or silver-based solders are used.

As shown schematically in FIG. 2 for a single feed line 11 and tworeturn lines 12, cooling liquid 13 flows into the impingement coolingdevice 1 via the feed line 11 of the supporting body 7 to the nozzleopenings 9 in the nozzle plate 5. Since the opening cross section of thenozzle opening 9 is smaller than the line cross section of the feed line11, the cooling liquid 13 emerges from the nozzle opening 9 at anaccelerated rate into the cutout 8 and impinges there on the rear side 3b of the carrier plate 3, which is thereby cooled. This impingementcooling is denoted in FIG. 2 overall by impingement area 14. The coolingliquid 13 bounces back then flows further within the cutout 8 radiallyoutward and via the through-channels 10 of the nozzle plate 6 into thereturn lines 12 of the supporting body 7.

The impingement cooling device 1 shown in FIG. 3 differs from FIG. 2 inthat here the cutout 8 in the distributor plate 5 is closed toward therear side 3 b of the carrier plate 3 by a base 17 of the distributorplate 5. The cooling liquid 13 impinges on the base 17 of thedistributor plate 3, so that the carrier plate 3 is not cooled directlyby the cooling liquid 13, but indirectly via the base 17 of thedistributor plate 3. Direct contact between the cooling liquid 13 and asolder located between the carrier plate 3 and the distributor plate 5is thereby avoided and the risk of corrosion is reduced.

The impingement cooling device 1 shown in FIG. 4 differs from thedevices shown in FIGS. 2 and 3 in that here the rear side 3 b of thecarrier plate 3 has the cutout 8′, which is open toward the front side 7a of the supporting body 7, and is secured directly on the front side 7a of the supporting body 7. The feed line 11 leads into the cutout 8′ inthe carrier plate 3, from which, in turn, the return lines 12 lead away.The cooling liquid 13 emerges from the feed line 11 directly into thecutout 8′ and impinges there on the rear side 3 b of the carrier plate3, which is thereby cooled.

The cutout 8′ is introduced into the rear side 3 b of the carrier plate3 for example by laser machining. This structured rear side 3 b of thecarrier plate 3 is then soldered onto the front side 7 a of thesupporting body 7 by hard solder. Finally, the required feed and returnlines 11, 12 are introduced into the supporting body 7 by spark erosion.Alternatively, the supporting body 7 may also be made up of individualperforated disks that are cut to size by a laser and soldered togetherto form a stack and the holes of which are in line with one another, toform the continuous feed and return lines 11, 12 in the stack.

The impingement cooling device 1 shown in FIG. 5 differs from FIG. 2 inthat the feed line 11 in the supporting body 7 is formed by a separate,free-standing tube 18 (for example of high-grade steel) arranged in athrough-channel 15 of the supporting body 7 to form an annular gap 16.In the supporting body 7 there runs only a single return line 12 that isformed by the annular gap 16 that is present between the tube 18 and thethrough-channel 15. The tube 18 reaches with its one, free end up to thecutout 8′ and is secured at its other, fixed end on the rear side of thesupporting body 7. Alternatively, the distributor plate 5 of FIG. 3 orthe carrier plate 3 of FIG. 4 may also be used.

Other Embodiments

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. An impingement cooling device for a laser disk,comprising a carrier plate having a front side and a rear side, whereinthe laser disk is secured on the front side of the carrier plate; animpingement cooling area for cooling the carrier plate by a coolingliquid; and a supporting structure having a front side and a rear side,wherein the rear side of the carrier plate is secured on the front sideof the supporting structure, and wherein the supporting structurecomprises a plurality of cooling liquid feed lines from which thecooling liquid emerges in a direction towards the rear side of thecarrier plate, and a plurality of cooling liquid return lines, whereinthe feed and return lines run parallel to one another in thelongitudinal direction of the supporting structure, wherein (i) thesupporting structure comprises in a region adjoining the rear side ofthe carrier plate a plurality of cutouts, or (ii) the rear side of thecarrier plate comprises a plurality of cutouts that are open toward thesupporting structure, or both (i) and (ii), and wherein the coolingliquid feed lines lead into the plurality of cutouts and the coolingliquid return lines lead away from the plurality of cutouts.
 2. Theimpingement cooling device of claim 1, wherein the carrier plate isdisk-shaped.
 3. The impingement cooling device of claim 1, wherein thecooling liquid emerges in a direction towards the rear side of thecarrier plate at right angles with respect to the rear side of thecarrier plate.
 4. The impingement cooling device of claim 1, wherein thecutouts in the supporting structure are open toward the rear side of thecarrier plate.
 5. The impingement cooling device of claim 1, wherein thecutouts in the supporting structure are closed toward the rear side ofthe carrier plate.
 6. The impingement cooling device of claim 1, whereinthe carrier plate is formed from diamond material and has a thickness ofat most 5 mm.
 7. The impingement cooling device of claim 1, wherein thecarrier plate is formed from diamond material and has a thickness of atmost 2 mm.
 8. The impingement cooling device of claim 1, furthercomprising a distributor plate having a front side and a rear side andcomprising cutouts; and wherein the supporting structure furthercomprises a supporting body that comprises the cooling liquid feed linesand the cooling liquid return lines, wherein the rear side of thecarrier plate is secured on the front side of the distributor plate, andwherein the rear side of the distributor plate is secured on thesupporting body.
 9. The impingement cooling device of claim 8, whereinthe cutouts in the distributor plate are open toward the rear side ofthe carrier plate and extend as through-openings from the front side tothe rear side of the distributor plate, and wherein the cooling liquidimpinges on the rear side of the carrier plate.
 10. The impingementcooling device of claim 8, wherein the cutouts in the distributor plateare closed toward the rear side of the carrier plate by a base of thedistributor plate, and wherein the cooling liquid impinges on the baseof the distributor plate.
 11. The impingement cooling device of claim 8,wherein the supporting body is formed of ceramic or hard metal and has athickness of at least about 0.5 cm
 12. The impingement cooling device ofclaim 8, wherein the supporting body is formed of ceramic or hard metaland has a thickness of between about 0.5 cm and about 10 cm.
 13. Theimpingement cooling device of claim 8, further comprising a nozzle platearranged between the distributor plate and the supporting body, whereinthe nozzle plate comprises nozzle openings that connect the respectivecooling liquid feed lines of the supporting body to the cutouts of thedistributor plate and are aligned in the direction of the rear side ofthe carrier plate, and through-openings that connect the cutouts in thedistributor plate to the cooling liquid return lines.
 14. Theimpingement cooling device of claim 8, wherein one or both of thedistributor plate or the nozzle plate is formed of diamond material,ceramic, or hard metal, and has a thickness of at least 0.3 mm
 15. Theimpingement cooling device of claim 8, wherein one or both of thedistributor plate or the nozzle plate is formed of diamond material,ceramic, or hard metal, and has a thickness of at least 0.5 mm.
 16. Theimpingement cooling device of claim 1, wherein the rear side of thecarrier plate has the cutouts and is secured on the front side of asupporting body comprising the cooling liquid feed lines and the coolingliquid return lines.
 17. The impingement cooling device of claim 16,wherein the supporting body is formed from ceramic or hard metal and hasa thickness of at least about 0.5 cm
 18. The impingement cooling deviceof claim 16, wherein the supporting body is formed from ceramic or hardmetal and has a thickness of between about 0.5 cm and about 10 cm. 19.The impingement cooling device of claim 8, wherein the cooling liquidfeed and the cooling liquid return lines are through-channels in thesupporting body.
 20. The impingement cooling device of claim 1, whereinthe carrier plate and components of the supporting structure aresoldered, glued, sintered, or bonded to one another.
 21. The impingementcooling device of claim 1, wherein each of the cooling liquid feed lineslead into a separate cutout in the distributor plate and are surroundedby a plurality of cooling liquid return lines that lead away from theseparate cutout in the distributor plate.
 22. A laser disk modulecomprising an impingement cooling device of claim 1 and a laser disksecured on the front side of the carrier plate of the impingementcooling device.